1. Field of the Technology
The technology presented herein relates to a layer forming apparatus for forming at least one layer of photosensitive layers of an electrophotographic photoreceptor by a dip coating method.
2. Description of the Related Art
In the art of electrophotography, image formation is carried out in the following manner. A surface of an electrophotographic photoreceptor (hereinafter referred to as “a photoreceptor”) is charged and then exposed to light so that an electrostatic latent image is formed. The electrostatic latent image is then developed by electrostatically depositing a toner on the surface of the photoreceptor on which a latent image is formed. A toner image is thus obtained and then transferred from the surface of the photoreceptor to a recording medium such as paper, and the toner image on the recording medium is fixed afterward. In forming the image, the toner is charged by frictional electrification and transported by a developer carrier such as a developing roller so that the toner is supplied to the surface of the photoreceptor. Residual toner, which is not transferred to the recording medium and remains on the surface of the photoreceptor, is physically scrapped off by a removing section and thus removed from the surface of the photoreceptor.
The photoreceptors in practical use at present may be classified roughly into photoreceptors using inorganic material and photoreceptors using organic material. The photoreceptors using inorganic material include photoreceptors using a selenium-series material such as amorphous selenium (a-Se) and amorphous arsenic selenium (a-As2Se3); and photoreceptors in which amorphous silicone (a-Si) and dye-sensitized zinc oxide (ZnO) are dispersed in binder resin. Further, the photoreceptors using organic material include a photoreceptor prepared by dispersing in polycarbonate resin or the like ingredient a phthalocyanine pigment or the like ingredient as a charge generating material and a hydrazone- or butadiene-series compound or the like ingredient as a charge transporting material.
Compared to the photoreceptors using inorganic material, the photoreceptors using organic material are higher in electrophotographic property, free from toxicity, and lower in manufacturing cost, by virtue of their applicability of a larger number of materials in various combinations.
As a method of manufacturing the photoreceptors using organic material (a method of forming a photosensitive layer), a dip coating method is generally adopted from the perspective of its relatively simple configuration of the apparatus and excellent productivity. In the dip coating method, a photosensitive layer is formed in a manner that a conductive substrate is dipped into a coating liquid (a photosensitive solution) containing a photosensitive substance, and then pulled up, followed by drying.
As described above, the dip coating method provides a relatively simple technique of production and enables to obtain a plurality of photoreceptors at one time. The dip coating method is thus suitable for mass production. However, such a dip coating method requires a large quantity of photosensitive solution in a coating tank, a pipe, etc. where a large amount of the photosensitive solution is not actually used and therefore remains. This poses a cost problem in small-lot production of various kinds. As a result, the study has started about how to reduce the coating liquid.
Moreover, in connection with the use of an organic solvent in the photosensitive solution, the organic solvent is added for adjustment of viscosity of the photosensitive solution since the organic solvent is liable to evaporate, and the photosensitive solution is circulated in order to collect for reuse the photosensitive solution which has overflowed at the coating occasion. In the circulation, a bubble is easily generated, thus inducing the study for various bubble-removing devices.
In a coating apparatus used for electrophotographic photoreceptor disclosed in Japanese Unexamined Patent Publication JP-A 9-269604 (1997), a deaeration mechanism for the overflowed coating liquid is provided just before a storage tank. However, the bubble arising in the coating liquid at the coating occasion is not taken into consideration although the bubble is generated from piping and liquid-supply pump of circulatory system.
In a coating apparatus used for electrophotographic photoreceptor disclosed in Japanese Unexamined Patent Publication JP-A 2001-272803, a centrifugal bubble-removing separator is provided between a liquid-supply pump and a coating tank. However, also in this case, the bubble is assumed to arise when the overflowed coating liquid is moving back, and the bubble arising on the downstream of the centrifugal bubble-removing separator is thus not taken into consideration.
Furthermore, in a non-sealed coating system, a smaller amount of the coating liquid in total will cause a relatively frequent contact of the coating liquid with the air, and a larger supply amount of the coating liquid will cause the air to be easily caught therein. Neither of JP-A 9-269604 and JP-A 2001-272803 disclose any approaches to the case where the total amount of the coating liquid is small.